For an aircraft, structures such as the wing and its high-light devices, horizontal and vertical tail planes, propellers, engine intakes, are prone to icing. This is undesirable when in use because the ice destroys the smooth flow of air over the structure, therefore decreasing the ability of the airfoil to perform its intended function and also increases drag and weight of the aircraft. Aircraft certified for flight in icing conditions are therefore normally fitted with de-icing and anti-icing systems, which when required, are used to remove (“de-ice”) or prevent (“anti-ice) a buildup of ice on aerodynamic surfaces of the aircraft structure.
Ice buildup is normally critical on the leading edge of such structures. If a buildup of ice is not prevented or removed from these surfaces, then the ice can lead to the degradation of the aerodynamic performance of the structure. The ice may also lead to a significant weight increase to the aircraft or potentially block an intake to an engine.
Different variations of such systems exist. Normally a pneumatic system is provided within a leading-edge structure. Such a system withdraws hot bleed-air from the engines via a manifold and pipes the air to the interior of the leading edge of the wing and slats and release it via a perforated “Piccolo” tube. Such arrangements are commonly used in large passenger aircraft but they have their disadvantages. Bleed air from the engine is normally bled off at high pressure and temperature. The piping used to route the bleed air as a result is made of high performance metallic alloys such as titanium, which increases the cost. The routing normally extends substantially over the entire wing span of the aircraft. An associated control and monitoring system consisting of actuatable valves, as well as pressure, temperature and overheating sensors is required in order to regulate the flow of hot air and to avoid structural damage in the event of valve malfunction. Overall, this means the systems normally carry a relatively high weight penalty, which is increased due to the surrounding structure also having to be sized adequately to support the piping. Furthermore, the integration of such systems into leading edge moveable slats, adds complexity to the design and in some cases it can limit the use of thin airfoil sections due to the required size of the piccolo tubing within the slat itself.
Electrically powered systems are also known. Such electrically powered systems are usually configured to draw current from an aircraft's electrical power generator in order to power heater mats or coatings that are embedded within or laminated directly to the outer skin of the wing leading edge or the leading edge slat. The mats are in direct contact so as to ensure adequate conduction of the heat energy to the airfoil surface by the heater mat or coating. An associated control and monitoring system consisting of temperature sensors is required in order to carefully regulate the temperature of the heater mat attached directly to the structure. The tolerances of this monitoring system are normally small because any overheating of the laminated heating mat can have an immediately impact the structure to which it is attached. Furthermore, having a heater mat or coating which is essentially part of the structure, results in a system which is difficult to repair without substantial disassembly of the surrounding structure, which may result in prolonging the amount of time that an aircraft is out of service.